1. Field of the Invention
The present invention relates to a gas stove which is adapted for cooking in office or home, and in particular, to a flat heating surface type gas stove wherein a heat-resisting glass top plate is used as a flat heating surface, thereby preventing flame from being exposed out of the heating surface during the heating operation thereof.
2. Description of the Related Art
The conventional gas stove is generally designed such that a substance to be heated is directly heated by the flame that is generated by the combustion of gas. Specifically, as shown in FIG. 5, a heating substance 4, such as a pot or a frying pan (skillet), which is supported by means of a pan support 3 is placed over the combustion burner 2 that is exposed out of the top plate 1 of the stove. In the case of a conventional stove of this type, since the burner and the pan support are exposed, the stove is required to be frequently cleaned, and at the same time, since the surface structure thereof is rather complicated, it is difficult to completely sweep away soils from the surface of stove. Additionally, since flame is exposed during heating, radiant heat is transmitted directly to a person using the stove, thus occasionally imparting a feeling of heat to the person. Therefore, the person using the stove is required to pay some degree of attention to ensure safety in dealing with the stove.
With a view to avoiding such an inconvenience, there has been proposed an electric stove, as shown in FIG. 6, which is constructed, as represented by an IH stove, a halogen stove or a radiant heat stove, such that the top plate 5 of stove is constituted by heat resistant glass such as ceramic glass, and that the heating substance 4 is heated by means of electromagnetic wave (including visible light and infrared ray) which is designed to pass through this glass top plate 5 as it is generated from a heater 6.
It is now studied to enable the same heating method as employed in the aforementioned electric stove to be realized in a gas stove where gas is employed as a fuel. However, since only the visible light and infrared rays generated through the combustion of gas can be utilized in heating a heating substance instead of directly utilizing the combustion gas, if the aforementioned method is adopted in a gas stove, the heating efficiency of such a gas stove would greatly deteriorate even if the gas stove is of an infrared burner type. Namely, it has been considered very difficult in such a gas stove to improve the heating efficiency thereof to a practically applicable level.
The present invention has been accomplished under the conditions explained above, and therefore, an object of this invention is to provide a novel flat heating surface type gas stove which is capable of heating a heating substance across a heat resistance glass at such high heating efficiency that is applicable to practical use in spite of the fact that the gas stove employs gas as a fuel, thus making it possible to overcome any inconvenience that may be brought about due to the exposure of flame, and to facilitate the cleaning of the gas stove.
Namely, the gas stove according to the present invention is a flat heating surface type gas stove, which fundamentally comprises a heat resistant glass top plate which is disposed over a burner, wherein a gas-permeable porous body is disposed below said top plate, a space between said top plate and a surface of said gas-permeable porous body is assigned to a combustion space, and combustion gas to be generated is designed to be discharged through said gas-permeable porous body.
It is known that when a high-temperature gas is passed through a gas-permeable porous body, thermal energy is transferred from the high-temperature gas to the porous body and is then radiated from the surface of the porous body (xe2x80x9cThe improvements on the combustion and radiant heat in porous solid bodyxe2x80x9d, a collection of articles 52-475, B-1136; Japan Society of Mechanical Engineers). By increasing the porosity of the porous body, or by employing a material of high emissivity as a porous body, the radiation from the porous body can be increased, thus lowering the temperature of porous body and rapidly lowering the temperature of gas. As a high-temperature gas is passed through a gas-permeable porous body, even though the temperature of gas on the gas inlet side of the porous body is high, the temperature of gas on the gas outlet side of the porous body is lower. Therefore, the radiation from the porous body can be effected selectively on the high-temperature gas side, i.e. the upstream side of gas.
According to the present invention, the flat heating surface type gas stove which is provided with a heat resistance glass top plate disposed over a burner is technically featured in that the aforementioned phenomenon to be realized by the use of a gas-permeable porous body. Therefore, it is now possible to obtain a flat heating surface type gas stove which is capable of exhibiting such high-heating efficiency that can be practically used in spite of the fact that the gas stove employs gas as a fuel.
Namely, in the case of the gas stove according to the present invention, the combustion heat from the burner is transmitted to a heating substance by two ways. First, by the energy of heat conduction originating directly from the heat resistant glass top plate (flat heating surface). Second, by the radiation energy originating from the surface of gas-permeable porous body, that can be generated as the combustion gas of high-temperature produced inside the combustion chamber is permitted to pass through the gas-permeable porous body which is disposed below the top plate. As a result, it is now possible, with this gas stove, to realize high heating efficiency.
Moreover, in the gas stove according to the present invention, since the surface to support and heat a heating substance, such as a pot or a frying pan, is flat, the cleaning can be easily performed even if this surface is soiled by boiled-over matter. Additionally, since the combustion space of this gas stove is substantially closed so that the flame of combustion gas is not permitted to exit from the combustion space, it is possible to ensure a high operational safety.
As for the material of gas-permeable porous body which enables the aforementioned combustion gas to pass therethrough, there is not any particular limitation as long as it has a predetermined heat resistance. However, it is more preferable that the material of gas-permeable porous body is capable of emitting a higher radiation toward the upstream side as a high-temperature gas is passed therethrough. Preferable examples of such a gas-permeable porous body are those which are formed into a porous body by making use of silicon carbide exhibiting a high emissivity (0.9 or more) or a material containing silicon carbide as a main component. For example, an aggregate of silicon carbide fibers or ceramic filters can be preferably employed as the material of gas-permeable porous body.
The surface of gas-permeable porous body is heated up to almost the same temperature as that of the combustion gas as the high-temperature combustion gas passes through the gas-permeable porous body, thereby radiating thermal energy. In the course of the passage of combustion gas across the gas-permeable porous body, the temperature of combustion gas is lowered to become a low temperature gas, which is then discharged out of the gas stove. Even this low temperature gas, the temperature thereof is maintained generally at 600. or so. Therefore, heat radiation is generated even on the gas outlet side, i.e. rear side of the gas-permeable porous body. The heat radiation thus generated is directed toward the exhaust side of the gas stove, thus resulting in a heat loss to the gas stove.
With a view to minimize this heat loss, there is provided another embodiment of gas-permeable porous body wherein a second gas-permeable porous body having a lower emissivity than that of the first mentioned gas-permeable porous body is laminated on the gas outlet side of the first mentioned gas-permeable porous body. As for the material of the second gas-permeable porous body also, there is not any particular limitation as long as it has a predetermined heat resistance. However, it is more preferable that the material of the second gas-permeable porous body is formed of silica/alumina-based ceramic exhibiting an emissivity ranging from 0.2 to 0.3 or a material containing as a main component such a silica/alumina-based ceramic. For example, an aggregate of silica/alumina-based ceramic fiber can be preferably employed. Alternatively, a ceramic filter exhibiting a relatively low emissivity can be employed as the second gas-permeable porous body.
According to the flat heating surface type gas stove of the present invention, there is not any particular limitation with regard to the burner to be employed therein. For example, the burner may be a pipe burner which is disposed to surround a region immediately above the gas-permeable porous body or a surface combustion type burner. In the case of the former burner, the flame ports thereof are preferably disposed in such a manner that the flame from each flame port can be horizontally ejected in the direction toward the center of the region immediately above the gas-permeable porous body. If a sufficient combustion of gas can be achieved with only primary air, the arrangement of the burner may be such as mentioned above. Generally however, when it is desired to achieve a desired combustion of gas with only a primary air, the blow-off of flame or the generation of unburnt gas is caused to occur. In order to prevent such phenomena, the burner should preferably be designed such that a secondary combustion air can be supplied in the vicinity of each of the flame ports. In any cases, it is preferable to provide the burner with a suitable flame stabilizing mechanism.
In a structure where a surface combustion burner is employed, the combustion surface thereof, together with the surface of gas-permeable porous body, is disposed so as to face the combustion space. As a result, the combustion heat of the surface combustion burner can be effectively conducted to the flat heating surface constituted by the heat resistant glass top plate. Preferably, the combustion surface of the surface combustion burner should be formed of a material exhibiting a high emissivity, such as silicon carbide or a material containing silicon carbide as a main component. In this case, in addition to the heating by way of heat conduction, the heating by way of radiation energy can proceed, thereby making it possible to realize high heating efficiency by the surface combustion burner.
If the surface combustion burner is to be employed, the combustion surface thereof may be disposed on the periphery of the surface of the gas-permeable porous body, or the gas-permeable porous body may be disposed on the periphery of the combustion surface of the surface combustion burner. In any cases, a high-temperature combustion gas from the surface combustion burner is permitted to be discharged through the gas-permeable porous body, during which the gas-permeable porous body is heated to a red hot state, thus radiating thermal energy.
According to another embodiment of the gas stove of the present invention, the gas stove essentially comprises a combustion gas passageway communicated with a space located on a downstream side of combustion gas flow channel of gas-permeable porous body; an air passageway for combustion, and a heat-exchanging means acting between the combustion gas passageway and the air passageway for combustion, wherein a mixed gas comprising a combustion gas and combustion air which has been heated through heat exchange thereof with the combustion gas by means of heat-exchanging means is designed to be fed to a burner. In the case of gas stove of this embodiment, the quantity of heat retained in the combustion gas after the passage thereof through the gas-permeable porous body is transferred via the heat-exchanging means to the combustion air to thereby perform exhaust heat recovery. As a result, the air thus heated up and the combustion gas is enabled to be mixed together to form a mixed gas, which is then transferred to the burner for the combustion thereof, resulting in improved heating efficiency as a whole.